Rat fever: the facts

Rat fever (leptospirosis) is an infectious disease caused by pathogenic bacteria called leptospires, which are maintained in nature in the kidneys of certain animals such as rats, pigs, cattle, rodents, canines, wild mammals and livestock. These organisms are transmitted directly or indirectly from animals to humans, consultant epidemiologists attached to the Epidemiology Unit of the Health, Nutrition and Indigenous Medicine Ministry said.

Some animal species have a commensal relationship with certain types of leptospires (serovars), i.e., natural hosts for those serovars, the consultant epidemiologists said.

These animals continuously excrete leptospires in urine, though they do not suffer from the disease. If other animals including humans are infected by the same serovars, they often become ill. If a natural host for a particular serovar is infected with another serovar, it may also develop the disease. Serovars found in rats and bandicoots are often identified as the cause for serious illness in humans.

Man is an incidental or accidental host. Exposure through water, soil, or foods contaminated by urine of affected animals is the most common route. A leptospire-contaminated environment caused by, for example, local agricultural practices (paddy cultivation) and poor housing and waste disposal gives rise to many sources of infection.

Leptospires enter the body through abraded or traumatized (injured) skin or nasal, oral, or eye mucous membranes. Ingestion of contaminated water can also lead to infection. After infection, they enter the blood and invade practically all tissues and organs, they said.

The diagnosis of leptospirosis should be considered in any patient presenting with an abrupt onset of fever, chills, conjunctival suffusion, headache, muscle tenderness (notable in calf and lumbar areas) and jaundice. The fatality rate is reported to range from less than five percent to 30 percent, and important causes of death include renal failure, heart failure and widespread hemorrhage. Liver failure is rare despite the presence of jaundice.

Knowledge of local epidemiology and varied clinical presentation and high index of suspicion are essential to make a diagnosis. Suspicion should be further increased if there is a history of occupational or recreational exposure. Confirmatory diagnosis is mainly by detecting antibodies (e.g., MAT). However, simple investigations like urine full report (albumin+) and the differential count of white blood cells (polymorpholeucocytosis) would help clinicians to make a probable diagnosis and also to decide on the need for hospital admission. For epidemiological and public health reasons also, laboratory support is important. Identifying serovars (serotyping) is costly, time consuming and the results are not likely to affect treatment of an individual patient. However, the resulting information is useful in investigating its source or potential reservoir, and planning and evaluating interventions.

Leptospirosis is a potentially serious but treatable disease. Treatment with effective antibiotics should be initiated as soon as the disease is suspected. Clinicians should never wait for the results of laboratory tests before starting treatment with antibiotics because serological tests do not become positive until about a week after the onset of illness, and the culture may not become positive for several weeks. Supportive care with strict attention to fluid and electrolyte balance is essential. Dialysis is indicated in renal failure. Heart failure can occur if medical treatment is not given on time.

Serovar-specific antibodies produced following infection are protective and a patient is immune to re-infection with the same serovar as long as the specific antibody titre is high enough. However, it will not protect against infection with other serovars. The bacteria live in the environment over a period of one month.

Preventive measures must be based on knowledge of high-risk groups and local epidemiological factors. It is very important to raise awareness about the disease among the risk groups, health care providers and general population, so that the disease can be recognised early and treated as soon as possible. If you are involved in occupations such as farming, mining, or cleaning drains and canals, please inform your area MOH or PHI. They will explain the specific precautions that can be taken to prevent contracting the disease.

The statistics

A total of 4,187 rat fever cases have been reported across the country in 2018. The highest number of cases (652) was reported in the Ratnapura district, while the second highest number of cases (589) was reported in the Kalutara district. The Galle district recorded a total of 384 cases of rat fever, while the Moneragala district recorded 319 cases during the same period. The Kegalle district recorded 311 rat fever cases. The highest number of rat fever cases this year (464) was reported in July and the second highest number (444) was reported in June.


Symptoms normally appear within five to 14 days following exposure to the germ. The range is between two to 30 days. Leptospirosis may present with a wide variety of clinical manifestations. These may range from a mild flu-like illness to a serious and sometimes fatal disease. It may also mimic many other diseases such as dengue fever, influenza, meningitis, and hepatitis. Jaundice is a relatively common symptom of leptospirosis, but is also found in many other diseases involving the liver.

The main and common symptoms of rat fever are abrupt onset of high fever, mild flu, chills, conjunctival suffusion, muscle tenderness (notable in the calf and lumber areas), intense headache, jaundice and decrease in passing urine.

Sri Lankan context

In Sri Lanka, leptospirosis is reported throughout the year.

High humidity and heavy rainfall intensify outbreaks because of widespread contamination by rodent urine in floodwater (rodents are displaced from their burrows and drains by the floodwater).

Annually, there are two peaks in the disease incidence at the time of the monsoons, a smaller one during March–May and a larger one during October–December.

This seasonal variability should be taken into consideration when planning prevention and control activities.

The vulnerable groups are farmers, persons who clean drains, persons who work in mines, marsh lands, and canals, and persons who swim or play in contaminated water.


* Remove rubbish and ensure areas around human habitation are free of rodents. Wild rats which live in the open environment are more dangerous than domestic rats.

* Keep animals away from gardens, playgrounds, sandboxes, and other places where children play.

* Where appropriate, wear protective clothing, knee-high boots, and gloves, and cover wounds with waterproof dressing.

* Use boiled water (chlorination is seldom useful, as virulent organisms withstand up to 4ppm; filtered water is also not safe).

*Avoid walking in floodwater.

* Doxycycline has been reported to give some protection against infection and disease. All vulnerable people in high risk categories should contact the nearest PHI or MOH office and obtain Doxycycline tablets (issued free of charge). They should drink plenty of water while working. The tablets give around 90 percent protection for a period of one week.


According to the Director of the Health Promotion Bureau, Colombo, and leading Consultant Epidemiologists Dr. Palihawadana, all information about leptospirosis and the drug used to prevent it (Doxycycline) can be obtained by dialing the hotline 0710 107107. The service is free of charge and available 24 hours a day. Well-qualified doctors and consultants answer inquiries.

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